PMC:2728203 / 15978-17566 JSONTXT

{"project":"2_test","denotations":[{"id":"18190927-14696379-62517987","span":{"begin":898,"end":900},"obj":"14696379"},{"id":"18190927-16552146-62517988","span":{"begin":1202,"end":1204},"obj":"16552146"},{"id":"18190927-17786152-62517989","span":{"begin":1260,"end":1261},"obj":"17786152"},{"id":"18190927-17786152-62517990","span":{"begin":1343,"end":1344},"obj":"17786152"}],"text":"The crystal and solution structures of the N-terminal domain of Nab2 were very similar for helices H1–H4 and superimposed with a Cα rmsd of 1.2 Å. However, the position of helix H5 varied significantly between the two structures as a result of a rigid-body rotation of the order of 25° (Fig. 4). This difference in the position of helix H5 could have been the result of crystal packing or might have been a consequence of partial proteolysis as it was only possible to trace the chain in the crystal structure as far as residue 94, whereas in the solution structure, this helix extended to residue 99. However, these differences are also consistent with the helix being only loosely associated with the rest of the structure, which is also consistent with the relatively few NOE connectivities to helices H1–H4 in the NMR data. Moreover, when the TLS (translation/libration/screw) rigid-body motion32 of the Nab2 N-terminal domain was modeled by assigning helices H1–H4 to one rigid body and helix H5 to another, the R-factor and Rfree derived from X-ray crystallography dropped substantially to 19.5% (from 20.7%) and 25.0% (from 26.4%), respectively. Analysis of the TLS motion using the TLDMD method33 indicated that the libration motions of helix H5 (20.1°2) were substantially greater than those of the helix H1–H4 core (libration of 4.6°2), consistent with helix H5 being substantially more mobile. Potentially, the movement of helix H5 might have a regulatory role in modulating the interactions between the Nab2 N-terminal domain and other components of the mRNA export machinery."}